1. Technical Field of the Invention
The present invention relates generally to an improved structure of a pressure sensor equipped with a pressure-sensing diaphragm to be exposed to pressure, for example, produced by combustion of fuel in an automotive internal combustion engine.
2. Background Art
There have been proposed pressure sensors which include a casing, a pressure-sensing diaphragm fitted in an end of the casing, and a pressure transmitting member disposed inside the casing. For example, Japanese Patent First Publication No. 2004-347387 and U.S. Pat. No. 5,471,883 disclose such a type of pressure sensors designed to measure the pressure in a cylinder of an automotive engine. The pressure-sensing diaphragm has an outer surface formed as a pressure-exposed surface which flexes when exposed to the pressure to be measured. Such flexing action is transmitted to the pressure transmitting member within the casing.
Within the casing, a pressure sensing device made up of strain gauges is disposed which is sensitive to the pressure, as transmitted from the pressure transmitting member, to output an electric signal indicative thereof.
When it is required to measure the pressure in a combustion chamber of an internal combustion engine, it will cause the pressure-exposed surface of the pressure-sensing diaphragm to be distorted by the heat, as produced by the combustion of fuel within the combustion chamber, thus resulting in an error in an output from the pressure sensor.
In order to eliminate the above problem, the pressure sensor, as taught in Japanese Patent First Publication No. 2004-347387, is designed to have the pressure-exposed surface shaped to decrease the amount of thermal distortion thereof. The pressure sensor, as taught in U.S. Pat. No. 5,471,883, is designed to have a cooling mechanism disposed inside the pressure-sensing diaphragm to decrease the amount of thermal distortion thereof.
Usually, the state of combustion in the engine, that is, the pressure or temperature in the combustion chamber of the engine varies depending upon the speed of or load on the engine, thus resulting in a variation in thermal distortion of the pressure-sensing diaphragm. The pressure sensor taught in the former publication, therefore, has a difficulty in reducing all types of distortion of the pressure-exposed surface arising from different states of combustion in the engine.
The pressure sensor, as taught in the latter publication, has the cooling mechanism, thus resulting in complexity of the structure and an increase in manufacturing cost thereof.